This invention relates to an impact tool comprising a housing, a cylinder axially movable in said housing, a hammer piston provided with pressurized fluid-operated reciprocable drive means arranged for reciprocably driving said hammer piston relative to said cylinder, a cushioning space for containing a recoil cushioning volume of air between the cylinder and the housing, and a pressure regulating means for controlling the supply and venting of air, to and from, respectively, the cushioning space and for balancing the pressure within the cushioning space relative to an actual forward feeding force applied to the housing in use of the tool.
An impact tool of the above type as disclosed in U.S. Pat. No. 3,727,700. This known tool, however, employs a vibration cushioning chamber which is continuously supplied with pressurized air and in which the air pressure is controlled by a spring biased relief valve mechanism. The opening pressure of the latter is determined by the degree of compression of the relief valve biasing spring, which in turn depends on the forward feeding force applied to the tool housing.
This type of pressure regulating means is, however, disadvantageous in that, in addition to the continuous air relief flow determined by the degree of compression of the relief valve biasing spring, it momentarily vents air to the atmosphere in order to avoid the build up of pressure peaks during recoil of the cylinder. Thus the above type of pressure regulating means does not permit the air in the cushioning chamber itself to be used as a resiliently deformable and, in use, deformed, spring means and thus itself, together with the cylinder and the housing, form a spring-mass vibration dampening system.
It is an object of the present invention to avoid or minimize one or more of the above disadvantages and to provide an impact tool with an improved pressure regulating means.